The present invention relates to sorption systems wherein a sorbate is alternately adsorbed onto and desorbed from a sorbent. More particularly, the invention relates to a coaxial waveguide applicator for uniformly transmitting electromagnetic energy, for example in the form of microwaves, to the sorbate/sorbent compound in order to quickly and efficiently desorb the sorbate from the sorbent.
In adsorption and absorption systems, which will be referred to herein as sorption systems, a first substance called a sorbate is alternately adsorbed (or absorbed) onto and then desorbed from a second substance called a sorbent. Specific sorbates and sorbents will usually be selected for a particular sorption system to produce a desired effect which is dependent on the affinity of the two substances. During an adsorption reaction, which is also referred to as the adsorb cycle or the adsorb portion of the sorption cycle, the sorbate is drawn onto and combines with the sorbent to produce a sorbate/sorbent complex, which will be referred to herein simply as a sorbate/sorbent compound. During the desorption reaction, which is also called the desorb cycle or the desorb portion of the sorption cycle, energy is supplied to the sorbate/sorbent compound to break the bonds between the sorbate and sorbent molecules and thereby desorb, or in other words separate or drive off, the sorbate from the sorbent. Substantial energy is imparted to the sorbate during the desorption reaction, and this energy can be harnessed for various uses.
An exemplary refrigeration sorption system may use a polar refrigerant, such as ammonia, as the sorbate and a metal halide salt, such as strontium bromide, as the sorbent. During the desorption reaction, which occurs in an enclosure called a sorber, the refrigerant molecules are driven off of the salt and into a relatively high pressure, high energy gaseous state. The refrigerant gas is subsequently condensed and then evaporated to produce a cooling effect. The evaporated refrigerant gas is then channeled back to the sorber, where it is once again adsorbed onto the salt in an adsorption reaction. The sorption cycle is repeated numerous times depending on the cooling requirements of the refrigeration system.
In certain prior art sorption systems, the desorption energy is supplied by a conventional heater. In such a system, a great deal of thermal energy is required to stochastically heat the sorbate/sorbent compound to the degree sufficient to break the bonds between the sorbate and sorbent molecules. As a result, the sorbate, sorbent and sorber are significantly heated, and substantial time and/or energy are required to remove this sensible heat and cool the sorber and sorbent before the next adsorption reaction can proceed.
In the refrigeration system described in the above-mentioned application, the desorption energy is supplied in the form of electromagnetic waves, such as radio frequency waves or microwaves, generated by, for example, a magnetron. Instead of heating the sorbate/sorbent compound, the electromagnetic waves selectively pump electrical energy into each sorbate-sorbent bond until the bond is broken and the sorbate molecule is separated from the sorbent molecule. Therefore, the sorbate, sorbent and sorber are not heated during the desorption reaction and consequently do not need to be cooled before the next adsorption reaction can proceed. As the desorption reaction is essentially isothermal, the overall performance of the refrigeration system is greatly improved.
It has been discovered that the efficiency and speed of the desorption reaction in an electromagnetic wave-activated sorption system can be increased by uniformly transmitting the electromagnetic waves to the entire volume of sorbate/sorbent compound contained within the sorber.
According to the present invention, a coaxial waveguide applicator is provided for uniformly transmitting electromagnetic waves to a sorbate/sorbent compound contained within a sorber to increase the efficiency and speed of the desorption reaction. In one embodiment of the present invention, the waveguide applicator comprises a sorber having a metallic tubular housing defining an outer conductor and first and second ends which are sealed to define an enclosure within the outer conductor, a sorbate/sorbent compound located within the enclosure, the sorber including a port through which a sorbate may be communicated into and out of the enclosure, a metallic inner conductor extending into the outer conductor and parallel to the longitudinal axis of the sorber, and means for coupling the inner and outer conductors to an electromagnetic wave generator, wherein electromagnetic waves transmitted by the electromagnetic wave generator are propagated through the enclosure by the inner and outer conductors to desorb the sorbate from the sorbate/sorbent compound.
According to a preferred embodiment of the invention, the coaxial waveguide applicator comprises a sorber having a metallic tubular housing defining an outer conductor and first and second ends, a non-metallic end plug positioned in the first end and a metallic end cap positioned in the second end to define a sealed enclosure within the outer conductor, a metallic inner conductor extending through the end plug, into the enclosure and toward the end cap generally parallel to the longitudinal axis of the sorber, a plurality of radial metallic fins connected to the inner conductor within the enclosure, a sorbate/sorbent compound positioned between the fins, the sorber including a port through which a sorbate may be communicated into and out of the enclosure, and means for coupling the inner and outer conductors to an electromagnetic wave generator, wherein electromagnetic waves transmitted by the electromagnetic wave generator are propagated through the sorbate/sorbent compound by the inner and outer conductors and the fins to desorb the sorbate from the sorbate/sorbent compound.
A sorption system according to the present invention preferably includes an electronic valve for controllably releasing the sorbate into the enclosure, an electronic switch for selectively actuating the electromagnetic wave generator and a programmable microcontroller for controlling the operation of the electronic valve and the electronic switch. After the adsorb cycle and prior to the desorb cycle, the pressure within the enclosure is relatively low; and in order to prevent a plasma ignition from occurring at the beginning of a desorb reaction, the microcontroller may be programmed to pulse the electronic valve briefly prior to actuating the electromagnetic wave generator to bring the pressure within the enclosure to a level sufficient to avoid the Geissler effect. Alternatively, the sorption system may include a power mosfet which is connected to the electromagnetic wave generator and controlled by the microcontroller to gradually increase the current in the electromagnetic wave generator to initiate desorption and thereby gradually increase the pressure in the enclosure before the full power of the electromagnetic wave generator is transmitted to the enclosure. Also, the sorption system of the present invention may include a temperature sensor connected to the electromagnetic wave generator and the microcontroller may be programmed to switch off the electromagnetic wave generator when its temperature rises a predetermined amount, which is an indication that the desorption reaction has been completed.
These and other objects and advantages of the present invention will be made apparent from the following detailed description, with reference to the accompanying drawings.